NOT saying this is the issue at all, but I'm only bringing it up b/c it ended up being our issue - our DS was always an AWFUL sleeper except a few short stints here and there so I thought I'd throw it out there & maybe you could pay attention/look for signs or ask your ped/doc to look at your DC at a check up..

We did co-sleeping off and on (mostly me when DH was at work) and I BFd until DS was about a year. We found that DS was waking alllll the time at night... seemed like he was always wanting a drink. You could let him CIO and he still wouldn't go back to sleep.... so we'd just let him drink. I tried leaving a cup with water b/c it wasn't about being hungry, it was the drink (like water). He had a dry mouth. He was mouth breating. Super long story short, he had a problem breathing at night and we took him to an ENT. He had big adenoids and tonsils. He had them out. A couple mos after ths surgery he started sleeping through the night (it got slowly better and better shortly after but it took a couple mos - maybe a little less than that like 4 weeks or six b/c after the surgery he was swollen from the procedure). Anyway he went from waking several times a night to now sometimes he'll go to bed (now 3) at 7pm if he's tired to, no kidding, he'll sleep anywhere from 9 until like 10 am.

NOT saying that's your issue, but I hear it's not uncommon. GL. Night waking is no fun at this age!!! I was lucky with my oldest. He slept straight through at 6 weeks!!!